The proposed experiments are designed to develop an animal model for the morphologic markers of hypoxia seen in victims of sudden infant death syndrome (SIDS). Episodes of obstructive apnea as well as diaphragmatic apnea have been described in infants who have gone on to die of SIDS, and episodes of abnormal respiration are thought to play an important role in the pathogenesis of this condition. Animal studies of the effects of repeated, brief episodes of hypoxia have not been reported. In experimental animals we will induce brief episodes of profound alveolar hypoxia by placing neonatal animals for a short period of time in an environment lacking oxygen. The conditions will be manipulated to mimic those present during episodes of prolonged apnea. After several weeks of daily, brief episodes of hypoxia, various tissues of these animals will be examined for tissue markers of hypoxia and hypoxemia using the methods that have been applied in postmortem studies of the tissues of SIDS victims. Preliminary experiments have shown that animals subjected to these hypoxic conditions do develop some tissue evidence of hypoxia. Other tissue changes described in SIDS victims will also be examined. The full development of such an animal model will greatly facilitate the understanding of the pathogenesis is SIDS and will help in the interpretation of portmortem findings in SIDS victims. In addition, information obtained from these animal studies regarding both the degree of respiratory abnormality and the tissue response to it will provide a scientific basis for the evaluation of living human infants to determine their risk of SIDS.